LEAK TESTER

Abstract

 Method for the in line leak testing of blow moulded containers wherein a conveyor line is fed with a continuous stream of blow moulded containers from a blow moulding machine, at least one measuring head is temporarily tightly connected to a first blow moulded container. The measuring head is moved in order to follow the movement of said first blow moulded container which is pressurized by a source of pressurized gas whereafter the source of pressurized gas is disconnected and said at least one measuring head is used to measure the pressure decay therein. The pressure decay is compared with stored data for the pressure decay of acceptable containers and an accept or non-accept signal is generated which implies proceeding or disposal of said first blow moulded container. Thereafter, the measuring head is moved against the moving direction of the conveyor line to a subsequent blow moulded container, and the process is repeated.

Description

[0001] The present invention belongs to the technical field of testing of blow moulded containers, and more particularly to the leak testing of blow moulded containers. More particularly, the present invention relates to a method for in line leak testing of blow moulded containers as defined by the preamble of claim 1. According to another aspect, the present invention concerns a machine for in line leak testing of blow moulded containers as defined by the preamble of claim 14.

Background

[0002] Quality control of blow moulded containers such as bottles, jars or canisters is a must in the blow moulding industry. Among others, leak testing is an important part of the quality control. Leak in containers may on the one hand lead to leaching of contained substance. On the other hand oxygen can penetrate the protective barrier which a blow moulded container represents for foodstuff or beverage. Presence of oxygen leads to loss of quality and frequently to the total loss of food or beverage products. Leak testing before the container is used in packaging applications is therefore an important task in order to avoid significant economic and ecological loss.

[0003] Depending on size and structure of the containers state-of-the-art blow moulding machines can provide several 10.000 containers per hour. Leak testing should not be a bottle neck and therefore be able to be fed with the production of the blow moulding. In order to do so in line leak testing has been developed. Such in line leak tester can take the whole production of a blow moulding machine, if necessary by splitting the production stream into two or more lines which run in parallel.

[0004] The rate of testing is extremely important. Investment costs are high in the blow moulding industry and productivity decides if a production line is profitable or not. The overall measuring time for a container in an in line leak tester should therefore be as short as possible.

[0005] US7559232B2 discloses a machine for leak testing melt blown bottles including a base plate which is provided with a vacuum. Leak testing is performed by applying vacuum to the bottom area of the bottle. Small leaks and cracks can be detected by comparing the reduced pressure versus time curve of each bottle is compared with data obtained from bottles without leak.

[0006] US3762213A discloses a method and an apparatus for detecting leaks in plastic bottles. The leak detector is sealingly engaged to the mouth of the bottle to be tested. Thereafter, a vacuum is drawn in the bottle. Reduced pressure versus time curve of each bottle is compared with data obtained from bottles without leak.

[0007] US3847013A describes filled-up and closed containers, such as aerosol cans, which are to be tested for leaks, and which are fed one after another each into a separate chamber. The chambers are moving and are hermetically sealed along their path between an inlet and an outlet station. A gas sampling station disposed forwardly of the outlet serves to take a gas sample out of each chamber. Gas samples from chambers with leaking containers will show a different sample composition than gas samples from chambers with tight containers.

[0008] US3938368A discloses leak testing of batteries which are moved along a first roller type conveyor to a leak testing station, above which is located an assembly having a plurality of nozzles matable over battery tell inlets. A first set of alternate cells is supplied with air at a given pressure, and metering means notes pressure change. Thereupon, the remaining alternate cells receive the same treatment. If the cells do not leak, the battery advances from the testing station along the roller conveyor. If a leak is detected, a push bar connected to cable means below the rollers ejects the battery transversely from the testing station along to a second conveyor, thereby isolating leaky batteries either for removal or further testing to locate more precisely the leak.

[0009] EP1320738A2 discloses a method for leak testing closed containers with at least one flexible wall area, by moving a biasing member relatively to said wall area and measuring and monitoring a biasing force on said container. Containers with leaks will provide different measured biasing forces than containers without leaks.

[0010] US2008072658A1 disclose a machine for leak testing melt blown bottles including a base plate which is provided with a vacuum. Leak testing is performed by applying vacuum to the bottom area of the bottle. Small leaks and cracks can be detected by comparing the reduced pressure versus time curve of each bottle is compared with data obtained from bottles without leak. The machine also includes a turntable assembly which makes in line testing feasible.

[0011] WO2004083800A1 discloses an in-line leak tester apparatus for detecting leaks in packages having a flexible cover such as contact lens packages. The flexible covers move in contact with an electromechanical switch when the atmospheric pressure surrounding the package is lowered.

[0012] Different methods for leak testing are known. Methods and machines for continuous leak testing of different items, including blow moulded products are known. However none of the cited documents discloses methods or machines which allow continuous leak testing which is fast enough to be fed with the output of a blow moulding machine.

[0013] There is a need to provide methods and machine for fast and continuous leak testing of blow moulded containers.

Objective

[0014] It is therefore an objective of the present invention to provide a method for fast and accurate in line leak testing of blow moulded containers. It is further an object to provide a machine for fast and accurate in line leak testing of blow moulded containers.

The present invention

[0015] The above mentioned objects are achieved by a method as defined in claim 1, representing a first aspect of the present invention.

[0016] According to another aspect, the present invention concerns a machine for fast and accurate in line leak testing of blow moulded containers as disclosed in claim 14.

[0017] Preferred embodiments of the different aspects of the invention are disclosed by the dependent claims.

[0018] With "continuous stream" as used herein is understood that the supply is basically uninterrupted, but that variations in the space between the containers for practical reasons may and will occur.

[0019] The present invention provides a method to perform in line leak testing of blow moulded containers which are moving on a conveyor line. The conveyor line is fed with a continuous stream of blow moulded containers from a blow moulding machine. The conveyor line is equipped with an incremental encoder. When the moving container passes a laser trigger photocell, the actual conveyor position is registered for that container. When said container reaches the measuring head idle position of the measuring head, the container and the movement of the measuring head are synchronized in order to start a measuring cycle. The measuring head is temporarily tightly connected to a first blow moulded container and moved in order to follow the movement of the first container which thereafter is pressurized by a source of pressurized gas, The source of pressurized gas is disconnected and the measuring head is used to measure the pressure decay in the first blow moulded container while following the movement of that container. In the next step th measured pressure decay is compared with stored data for the pressure decay of acceptable containers and an accept or non-accept signal is generated.

[0020] In some embodiments, a number of measuring heads are arranged in a group comprising two, three, four or more measuring heads, moving in unison or together to test two, three, four or more blow moulded containers simultaneously.

[0021] Accepted containers proceed on the conveyor belt, rejected containers are disposed. According to the present invention the measuring head is thereafter moved against the moving direction of the conveyor line to a subsequent blow moulded container, is tightly connected to said subsequent blow moulded container, is moved in order to follow the movement of said subsequent blow moulded container and is used to perform in line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal for said subsequent blow moulded container.

[0022] In one embodiment of the present invention, the measuring head is moved to an idle position before it is moved again and tightly connected to the subsequent blow moulded container.

[0023] If time allows it, the measuring head is moved to the entry point of the containers before connecting to another (subsequent) container to initiate another measurement. In general, typically the measuring heads are moved as close to the entry point as time allows before connecting to subsequent containers for new measurements. Herein is inherently understood that when a series of containers reaches the entry point with no interruptions or extra space between any two containers, the measurements may commence at any point downstream of the entry point as long as there is still sufficient area left to perform a measurement satisfactorily. On the other hand, when an interruption or extra space between two containers occur, the measuring head of heads will again have time to move all the way back to the entry point and start new measurements from there.

[0024] In another embodiment, the idle position is located close to the entry point of the fed containers.

[0025] Below, the present invention is described in form of a few non-limiting embodiments illustrated by figures, in which

Figures 1A-1G shows schematically a side view of a leak-testing station with one measuring head according to the present invention in a number of situations, chronologically arranged

Figures 2A-E shows schematically a side view of a leak-testing station with three measuring heads according to the present invention in a number of situations, chronologically arranged.

Figures 3A and 3B shows schematically a side view of a specific feature of the leak-testing station shown in Figure 2.

Figure 4 shows a diagram illustrating functionality of the present invention.

[0026] The terms "right", "left", "right-most" and "left-most" as used herein, are only in relation to the drawings, not intended to be general statements.

[0027] Figure 1A shows a schematic side view of a device according to the present invention in the form of a leak-testing station 10. A container 11 is about to enter the leak-testing station 10 on a conveyor belt 12. A measuring head 13 with connections to a source of pressurized gas (not shown) is suspended from a rail 14 via a carrier wheel 15 and a connection arm 16 which is shown as telescopic but may have any functional configuration. A pressure sensor 17 is arranged within the measuring head 13; it may as an alternative be arranged outside the measuring head 13 but in fluid connection therewith. The container is visualized as a bottle, but can have other forms as long as it exhibits an opening accessible from above. The connection between the connection arm 16 and the rail 14 can also have any functional configuration.

[0028] As shown in Fig. 1, the pressure head is in an idle or stand by position, i.e. to the far right in the drawing and slightly elevated (telescope retracted) so as to allow the container to move into a position below the pressure head without bumping into it.

[0029] While not shown, the far right point of the conveyer belt is in communication with an upstream conveyer belt or the like feeding containers to the test station 10

[0030] In Fig. 1B the container has moved to a position within the testing station, has been detected and the pressure head has initiated a movement in the same direction with the same approximate speed and initiated a lowering of the head towards the opening at the container top. The small vertical arrow indicates that the measuring head is moving downwards.

[0031] In Fig. 1C the measuring head is tightly connected to the opening of the container and at this point the container is immediately filled with air or other gas from a pressurized source thereof, via the measuring head to a predetermined pressure.

[0032] In Fig. 1D, the pressure source has been disconnected and the measurement of pressure decay is initiated. As indicated by the comparatively short distance travelled from the position of the container in Fig. 1C, the pressurizing of the container is a quick operation. In fact, it may be even quicker than visualized by Figs. 1C and 1D.

[0033] Fig. 1E shows the point at which the measurement is to be terminated. As shown, the leak-testing station has a width that is more than sufficient for measurements that are initiated at the entry point of the containers, which is beneficial for reasons explained below.

[0034] Fig. 1F shows that the measuring head has been disconnected from the container and is no longer moving away from the entry point while the container naturally continues to the left.

[0035] Figure 1G shows the measuring head returning back to the entry point or idle position, which it can safely do since in this particular case no further container is about to enter the leak-testing station.

[0036] Figure 2A shows an embodiment of a leak-testing station according to the present invention comprising three measuring heads 13, all parked at the entry point. A container A is about to enter the station.

[0037] In Figure 2B, a moment later, two containers A, B have entered the leak-testing station, A being tightly connected to the left-most measuring head and in the process of being pressurized, B about to be connected to the second measuring head while the third measuring head is still idle.

[0038] In Figure 2C a third bottle C has entered the leak-testing station and is about to be connected to the third measuring head. As shown, the distance between container B and C is larger than the distance between container A and B, reflecting a small "interruption" in the feed of containers and the third measuring head has been adapted to this increased distance. In the meantime, measurement is being performed on container A while container B has been pressurized.

[0039] As shown by Figure 2D, container A has reach a position similar beyond that at which the measurement was terminated in the embodiment of Figure 1 (Fig .1E). However, since the measuring head connected to container A cannot return before also the measurements of containers B and C are completed. There is therefore an option to continue to measure pressure drop in container A as well, an option that is sensible to use to the extent that added measuring time also will contribute to added certainty of the measurement and the conclusion on accepting or rejecting the container.

[0040] Fig. 2D shows a situation in which three subsequent containers D, E, F follows containers A, B, C so close that the measuring heads do not have the time to move all the way back to the entry point, but initiate the process at the point illustrated, all three heads moving down to connect the point shown, a distance from the entry point.

[0041] If even additional containers arrive without interruption, a situation may occur in which the point at which the measurement can be initiated, is so far from the entry point and so close to the discharge point from the leak-testing station 10 that the time for measurement becomes critically small. If or when that occurs, the speed of the conveyer belt 12 may be automatically reduced to allow sufficient time for measurement. When an interruption occurs, and the measuring heads again have the time to move back to the entry point, the speed can again be raised to normal.

[0042] Now, we are referring to Figures 3A and 3B. If containers arrive in a certain pattern, it may be more convenient to let the right-most measuring head rest in the idle position even when there is a container on the conveyer belt which could be tested by that measuring head, due to the fact that it is more sensible use of the resources to be able to return the other heads earlier, and instead let the left-most measuring heads test the container in question as the first one of the next cycle of movement. This is illustrated by Fig 3A in the sense that container I is not tested by the right-most measuring head even if it could. Instead, when the testing is done on containers G and H, all the two measuring heads performing the testing on containers G and H returns and all three measuring heads go into action to test containers I, J and K simultaneously.

[0043] Figure 4 shows a typical pressure versus time curve for leak testing by connecting a blow moulded container to a measuring head and a source of pressurized gas. A maximum pressure is reached at T₀. After the source of pressurized gas is disconnected a pressure decay occurs until T₁ is reached. The straight line shows the pressure decay of a container which can still be acceptable at T₁. Pressure decay is caused by delayed volume increase of the bottle (plastic deformation) and/or unavoidable pressure loss between measuring head and container. The interrupted line shows the pressure decay of a container which has to be rejected already at T₁ due significant leakage of pressurized gas. The pressure decay is further measured until T₂ is reached. The straight line shows a pressure decay which flattens. The container is accepted. The interrupted line shows an unacceptable pressure drop which does not flatten. This container has to be rejected.

[0044] While we above have shown embodiments of one and three measuring heads, other embodiments are feasible, such as four and even more measuring heads within the same leak-testing station.

[0045] In some embodiments, the blow moulded containers have a volume of at least 0.5L, or at least 2L or at least 10L.

[0046] In some embodiments, the measuring head is tightly connected to the blow moulded container for less than 3 seconds, or less than 2 seconds or even less than 1 second.

[0047] In certain embodiments the rate of leak tested bottles is at least 100 per minute, or at least 600 per minute or at least 1200 per minute.

[0048] In some embodiments, the blow moulded containers are fed in a variable sequence on the conveyor line, e.g. due to deviations in the blow moulding machine, in which case the distances between two or more measuring heads are adapted to the actual (random) gaps between the containers.

[0049] In some embodiments the position of the group of measuring heads is adapted to block gaps occurring in the sequence of containers on the conveyor line due to batch wise production of the containers. Modern blow moulding machines operate frequently several blow moulding heads in parallel and feed more or less tight blocks of containers onto the conveyor belt. After such a block of containers there is frequently a gap until the next block of containers is fed onto the conveyor belt.

[0050] In particular embodiments, the block gaps occurring in the sequence of containers on the conveyor line are used to move the group of measuring heads against the moving direction of the conveyor line and to move the group of measuring heads close to the idle position or to move the group of measuring heads to the idle position.

[0051] In some embodiments, after the accept or non-accept signal is generated, at least one measuring head is moved to and hold at an idle position and the remaining heads are tightly connected to subsequent blow moulded containers. Such a set-up allows a measurement with higher sensitivity compared to the set-up when all measuring heads are tightly connected to blow moulded containers.

[0052] In a particular embodiment all measuring heads are tightly connected for a prolonged time period to subsequent blow moulded containers on the conveyor line. This set-up allows to perform a leak testing with higher accuracy compared to when the blow moulded containers are fed in a tight sequence on the conveyor line. Leak testing with higher accuracy reduces the number of false generated non-accept signals.

[0053] In some embodiments, the measuring heads in the machine for in line leak testing of blow moulded containers are connected to a source of pressurized gas wherein the connections can be opened and closed by automatic valves.

[0054] It should be emphasized that the drawings are just illustrative for the purpose of the general principles of the invention, and that actual design of the elements shown will deviate significantly from these simple schematic drawings.

Claims

1. Method for the in line leak testing of blow moulded containers wherein a conveyor line is fed with a continuous stream of blow moulded containers from a blow moulding machine, at least one measuring head is temporarily tightly connected to a first blow moulded container, said at least one measuring head is moved in order to follow the movement of said first blow moulded container, said first blow moulded container is pressurized by a source of pressurized gas whereafter the source of pressurized gas is disconnected and said at least one measuring head is used to measure the pressure decay in said first blow moulded container while following the movement of said first blow moulded container, said measured pressure decay is compared with stored data for the pressure decay of acceptable containers and an accept or non-accept signal is generated which implies proceeding or disposal of said first blow moulded container characterized in that the at least one measuring head thereafter is moved against the moving direction of the conveyor line to a subsequent blow moulded container, is tightly connected to said subsequent blow moulded container, is moved in order to follow the movement of said subsequent blow moulded container and is used to perform in line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal for said subsequent blow moulded container.

2. Method according to claim 1 characterized in that the measuring head is moved to an idle position before it is moved and tightly connected to the subsequent blow moulded container.

3. Method according to claim 1 or 2 characterized in that the idle position is located close to the entry point of the fed containers.

4. Method according to claim 1 to 3 characterized in that measuring heads are arranged in a group comprising two, more preferred three and most preferred four or more measuring heads, moving in unison to test two, more preferred three and most preferred four or more blow moulded containers simultaneously.

5. Method according to any of the preceding claims characterized in that the blow moulded container has a volume of at least 0.5L, more preferred at least 2L and most preferred at least 10L.

6. Method according to any of the preceding claims characterized in that the measuring head is tightly connected to the blow moulded container for less than 3 seconds, more preferred less than 2 seconds and most preferred less than 1 second.

7. Method according to any of the preceding claims characterized in that the rate of leak tested bottles is at least 100 per minute, more preferred at least 600 per minute and most preferred at least 1200 per minute.

8. Method according to any of the preceding claims characterized in that the blow moulded containers are not fed in a tight sequence on the conveyor line due to deviations in the blow moulding machine and the distance between two or more measuring heads is adapted to random gaps between the containers.

9. Method according to any of the claims 4 to 8 characterized in that the position of the group of measuring heads is adapted to block gaps occurring in the sequence of containers on the conveyor line due to batch wise production of the containers.

10. Method according to any of the preceding claims characterized in that the block gaps occurring in the sequence of containers on the conveyor line are used to move the group of measuring heads against the moving direction of the conveyor line, preferably to move the group of measuring heads close to the idle position and most preferred to move the group of measuring heads to the idle position.

11. Method according to claim 8 to 10 characterized in that after the accept or non-accept signal is generated at least one measuring head is moved to and hold at an idle position and the remaining heads are tightly connected to subsequent blow moulded containers which are measured with higher sensitivity compared to when all measuring heads are tightly connected to blow moulded containers.

12. Method according to claim 8 to 10 characterized in that all measuring heads are tightly connected for a prolonged time period to subsequent blow moulded containers on the conveyor line in order to perform a leak testing with higher accuracy compared to when the blow moulded containers are fed in a tight sequence on the conveyor line.

13. Method according to claim 12 characterized in that said leak testing with higher accuracy reduces the number of false generated non-accept signals.

14. Device (10) for in line leak testing of blow moulded containers comprising a conveyor line fed with a continuous stream of blow moulded containers from a blow moulding machine, at least one measuring head arranged to move in parallel with the blow moulded containers and to temporarily tightly connect with a first blow moulded container and movable in order to follow the movement of said first blow moulded container, wherein the measuring head is equipped to pressurize the first blow moulded container and to measure the pressure decay in said first blow moulded container while following the movement of said first blow moulded container, a control unit equipped to compare the measured pressure decay with stored data for the pressure decay of acceptable containers and to generate an accept or non-accept signal which implies proceeding or disposal of said first blow moulded container characterized in that the at least one measuring head is equipped to be moved against the moving direction of the conveyor line to a subsequent blow moulded container, tightly connected to the subsequent blow moulded container, moved in order to follow the movement of said subsequent blow moulded container, used to perform in line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal said for the subsequent blow moulded container.

15. Machine for in line leak testing of blow moulded containers according to claim 14 characterized in that the measuring head is connected to a source of pressurized gas wherein the connection can be opened and closed by an automatic valve.

Amended claims

Amended claims in accordance with Rule 137(2) EPC.

1. Method for the in line leak testing of blow moulded containers wherein a conveyor line is fed with a continuous stream of blow moulded containers from a blow moulding machine, at least one measuring head is temporarily tightly connected to a first blow moulded container, said at least one measuring head is moved in order to follow the movement of said first blow moulded container, said first blow moulded container is pressurized by a source of pressurized gas whereafter the source of pressurized gas is disconnected and said at least one measuring head is used to measure the pressure decay in said first blow moulded container while following the movement of said first blow moulded container, said measured pressure decay is compared with stored data for the pressure decay of acceptable containers and an accept or non-accept signal is generated which implies proceeding or disposal of said first blow moulded container characterized in that the at least one measuring head thereafter is moved against the moving direction of the conveyor line to a subsequent blow moulded container, is tightly connected to said subsequent blow moulded container, is moved in order to follow the movement of said subsequent blow moulded container and is used to perform in line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal for said subsequent blow moulded container, wherein measuring heads are arranged in a group comprising two, more preferred three and most preferred four or more measuring heads, moving in unison to test two, more preferred three and most preferred four or more blow moulded containers simultaneously, wherein random gaps between the containers are handled by adapting the distance between two or more measuring heads to the random gaps between the containers and block gaps in the sequence of containers on the conveyor line occurring due to batch wise production of the containers are handled by adapting the position of the group of measuring heads to the block gaps.

2. Method according to claim 1 characterized in that the measuring head is moved to an idle position before it is moved and tightly connected to the subsequent blow moulded container.

3. Method according to claim 1 or 2 characterized in that the idle position is located close to the entry point of the fed containers.

4. Method according to any of the preceding claims characterized in that the blow moulded container has a volume of at least 0.5L, more preferred at least 2L and most preferred at least 10L.

5. Method according to any of the preceding claims characterized in that the measuring head is tightly connected to the blow moulded container for less than 3 seconds, more preferred less than 2 seconds and most preferred less than 1 second.

6. Method according to any of the preceding claims characterized in that the rate of leak tested bottles is at least 100 per minute, more preferred at least 600 per minute and most preferred at least 1200 per minute.

7. Method according to any of the preceding claims characterized in that the block gaps occurring in the sequence of containers on the conveyor line are used to move the group of measuring heads against the moving direction of the conveyor line, preferably to move the group of measuring heads close to the idle position and most preferred to move the group of measuring heads to the idle position.

8. Method according to claim 8 to 10 characterized in that after the accept or non-accept signal is generated at least one measuring head is moved to and hold at an idle position and the remaining heads are tightly connected to subsequent blow moulded containers which are measured with higher sensitivity compared to when all measuring heads are tightly connected to blow moulded containers.

9. Method according to claim 8 to 10 characterized in that all measuring heads are tightly connected for a prolonged time period to subsequent blow moulded containers on the conveyor line in order to perform a leak testing with higher accuracy compared to when the blow moulded containers are fed in a tight sequence on the conveyor line.

10. Method according to claim 12 characterized in that said leak testing with higher accuracy reduces the number of false generated non-accept signals.

11. Device (10) for in line leak testing of blow moulded containers comprising a conveyor line fed with a continuous stream of blow moulded containers from a blow moulding machine, at least one measuring head arranged to move in parallel with the blow moulded containers and to temporarily tightly connect with a first blow moulded container and movable in order to follow the movement of said first blow moulded container, wherein the measuring head is equipped to pressurize the first blow moulded container and to measure the pressure decay in said first blow moulded container while following the movement of said first blow moulded container, a control unit equipped to compare the measured pressure decay with stored data for the pressure decay of acceptable containers and to generate an accept or non-accept signal which implies proceeding or disposal of said first blow moulded container characterized in that the at least one measuring head is equipped to be moved against the moving direction of the conveyor line to a subsequent blow moulded container, tightly connected to the subsequent blow moulded container, moved in order to follow the movement of said subsequent blow moulded container, used to perform in line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal said for the subsequent blow moulded container.

12. Machine for in line leak testing of blow moulded containers according to claim 14 characterized in that the measuring head is connected to a source of pressurized gas wherein the connection can be opened and closed by an automatic valve.

Drawing